A large truck, such as a dump truck, has a two-shaft structure for supporting the rear wheels in order to evenly support a load, particularly while traveling on a rough unpaved road.
A rear-wheel suspension device of a large truck, which has a two-shaft structure for supporting the rear wheels, includes a pair of rubber springs, which are mounted to a rear-wheel front axle and a rear-wheel rear axle, and a leaf spring, which extends in the forward-and-backward direction such that two opposite ends thereof are connected to the rubber springs.
A trunnion base, which includes a trunnion shaft, is provided at the middle in the longitudinal direction of the leaf spring. The trunnion base is coupled to a vehicle body frame, and a U-bolt saddle (an under saddle or a lower saddle) is rotatably coupled to the trunnion shaft and coupled to the middle portion of the leaf spring, together with a spring bracket (an upper saddle), by fastening U-bolts and nuts, in order to fixedly support the middle portion of the leaf spring.
The leaf spring may be constituted by multiple steel plates, or may alternatively be embodied as a composite leaf spring, which is formed in a unitary body containing glass fiber or carbon fiber. The leaf spring, which is constituted by multiple steel plates, is advantageous in terms of high durability for a given price, and the composite leaf spring is advantageous in terms of reduction in weight and improvement of fuel efficiency.
In the case of the leaf spring constituted by multiple steel plates, the steel plates crack and make a loud noise as the durability thereof deteriorates, making it possible for a user to be easily aware of the replacement time and to easily monitor the progression of cracks with naked eyes.
However, the composite leaf spring is damaged as the durability thereof deteriorates in a manner such that delamination, that is, separation of layers occurs one by one from the outermost layer of the top surface or the bottom surface of the composite leaf spring toward the inner layers. Therefore, the driver is not able to easily recognize the replacement time of the composite leaf spring auditorily or visually, which causes frequent occurrence of accidents attributable to damage to the composite leaf spring.
The information disclosed in this Background section of the disclosure is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.